Crossover Study of Zafirlukast in Preventing Allergen-induced Signs and Symptoms in Response to Cat Dander Challenge

The goal of this clinical trial is to test the hypothesis that pre-treatment with a nasal dose of Zafirlukast works well in blocking the signs and symptoms of cat dander in patients sensitive to cat dander. The main question it aims to answer is: • What is the difference in the symptoms of patients pre-treated with Zafirlukast and patients treated with a placebo (a look-alike substance that contains no active drug) when exposed to cat dander? Participants will screened to see if they qualify for the study based on their reaction to being exposed to cat dander and medical history. If they qualify, they will make two more visits to the allergy center, where they will be pre-treated with either Zafirlukast or a placebo and exposed to cat dander, then observed for four hours. Participants will * First be screened for their medical history, the medication they take, and other factors to see if they qualify for the study. * Participants will then be exposed to a fixed dose of cat dander to test their baseline change in TNSS. Some patients may need to return for a higher dose of cat dander. * On the next visit, some participants will be pre-treated with Zafirlukast and the rest with a placebo, then they will be exposed to cat dander. Their symptoms will be observed. * On the final visit, participants who were pre-treated with Zafirlukast on their last visit will be given a placebo. Participants who were pre-treated with a placebo on their last visit will be given Zafirlukast. All participants will then be exposed to cat dander and their symptoms will be observed.

The goal of this clinical trial is to test the hypothesis that pre-treatment with a nasal dose of Zafirlukast works well in blocking the signs and symptoms of cat dander in patients sensitive to cat dander. The main question it aims to answer is: • What is the difference in the Total Nasal Symptoms Score between patients pre-treated with Zafirlukast and patients treated with a placebo (a look-alike substance that contains no active drug)? The Total Nasal Symptom Score (TNSS; possible score of 0-12) is the sum of 4 individual subject-assessed symptom scores for * rhinorrhea (runny nose) * nasal congestion (stuffy nose) * nasal itching * sneezing Each of these are evaluated using a scale of * 0=None * 1=Mild * 2=Moderate * 3=Severe Participants will * First be screened for their medical history, the medication they take, and other factors to see if they qualify for the study. * Participants will then be exposed to a fixed dose of cat dander to test their baseline change in TNSS. Some patients may need to return for a higher dose of cat dander. * On the next visit, some participants will be pre-treated with Zafirlukast and the rest with a placebo, then they will be exposed to cat dander. Their symptoms will be observed. * On the final visit, participants who were pre-treated with Zafirlukast on their last visit will be given a placebo. Participants who were pre-treated with a placebo on their last visit will be given Zafirlukast. All participants will then be exposed to cat dander and their symptoms will be observed.